Nanosecond laser-based high-throughput surface nano-structuring (nhsn) process

ABSTRACT

Embodiments of the present invention are directed to a surface modified metal piece comprising a first major surface, wherein at least one portion of the first major surface: comprises the reaction product of a surface modifier; has a random micro- and nanoscale structure; and has at least one of a water contact angle when exposed to water of at least about 120° and a spectral reflectance of less than about 25% within the visible spectrum. Other embodiments relate to processes and methods for making such a surface modified metal piece.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalAppl. Ser. No. 62/547,999, filed Aug. 21, 2017, which is incorporated byreference as if set forth herein in its entirety.

BACKGROUND OF THE INVENTION

Existing laser-based surface texturing methods often use ultrashortpulse lasers (e.g., femtosecond or picosecond pulse lasers), to generateperiodic micro-/nano-scale features necessary for the super-hydrophobicor anti-reflective surfaces. Such fabrication methods scan the materialsurface at a very fine spatial resolution to create hierarchical micro-and nano-scale structures leading to an extremely low throughput. Afterultrashort laser texturing, a chemical surface treatment process oftenensues to reduce the surface energy and produces super-hydrophobicity.New methods are therefore needed for creating surfaces having, amongother features, super-hydrophobicity given the low throughput ofexisting methods.

SUMMARY OF THE INVENTION

Embodiments described herein relate generally to a nanosecondlaser-based high-throughput surface nanostructuring (nHSN) process toscale up the nano-structuring speed for a large surface area forengineering metal alloys. The nHSN process comprises two steps: (1) ahigh energy nanosecond pulse laser scans the material surface containedunder water using a large spatial increment and a fast processing speed;and (2) the laser textured surface is further chemically treated. Randomnanoscale surface structures are achieved from the nHSN process. Surfacetests of wettability and reflectance demonstrated that the processedsurfaces are, among other things, super-hydrophobic and highlyanti-reflective within the visible and infrared spectra for variousengineering metal alloys including steels, aluminum alloys, titaniumalloys, and magnesium alloys. Test results showed that the nHSN processproduces super-hydrophobic or highly anti-reflective surfaces over awide range of laser parameters. It was further demonstrated that theprocessed surfaces are mechanically enhanced with microhardnessincreased by about 20%. Compared with the existing ultrashortlaser-based surface texturing techniques, the nHSN process significantlyincreases the processing rate from hundreds of minutes per square inchto seconds per square inch, and also enables large area processing forpractical throughput.

DESCRIPTION OF THE DRAWINGS

The drawings illustrate generally, by way of example, but not by way oflimitation, various embodiments discussed in the present document.

FIG. 1 is an optical shadowgraph obtained using the CMOS camera.

FIG. 2 is a schematic representation of the instruments used todetermine the spectral reflectance for the at least one portion of thefirst major surface.

FIG. 3 is scanning electron microscope (SEM) micrographs of the surfacestructures prepared using existing laser-based surface texturingtechniques. (a) Laser-induced periodic surface structures (LIPSS) (Cunhaet al. 2013); (b) hierarchical structure consisting of trenchmicropattern (Martinez-Calderon et al. 2016).

FIG. 4 is scanning electron microscope (SEM) micrographs of various AISI4130 steel specimens.

FIG. 5 is a schematic representation of the process flow of nanosecondlaser-based high-throughput surface nano-structuring (nHSN).

FIG. 6 is a schematic representation of laser scanning path duringwater-confined nanosecond laser texturing (wNLT).

FIG. 7 is a schematic representation of the experimental setup for wNLT.

FIG. 8 is a photograph of still water droplets formed onsuperhydrophobic AA-6061 specimen surface produced by the nHSN processof the various embodiments described herein.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to certain embodiments of thedisclosed subject matter, examples of which are illustrated in part inthe accompanying drawings. While the disclosed subject matter will bedescribed in conjunction with the enumerated claims, it will beunderstood that the exemplified subject matter is not intended to limitthe claims to the disclosed subject matter.

Embodiments described herein relate to a surface modified metal piececomprising: a first major surface, wherein at least one portion of thefirst major surface: comprises the reaction product of a surfacemodifier; has a random micro- and nanoscale structure; and has at leastone of a water contact angle when exposed to water of at least about120° and a spectral reflectance of less than about 25% within thevisible spectrum. In some embodiments, at least one portion of the firstmajor surface comprising the reaction product of the surface modifierhas a water contact angle when exposed to water of at least about 120°and a spectral reflectance of less than about 30% within the visiblespectrum.

In some embodiments, at least one portion of the first major surfacecomprising the reaction product of the surface modifier has a watercontact angle when exposed to water of at least about 125°; at leastabout 130°; at least about 135°; at least about 140°; at least about145°; or at least about 150°. In some embodiments, at least one portionof the first major surface comprising the reaction product of thesurface modifier has a water contact angle when exposed to water ofabout 120° to about 170°; about 130° to about 170°; about 140° to about160°; about 150° to about 170°; about 150° to about 160°; or about 150°to about 165°.

The water contact angle (WCA) for the at least one portion of the firstmajor surface can be measured in any suitable way. One method formeasuring the water contact angle for the at least one portion of thefirst major surface involves using a contact angle goniometer (e.g., aRame-Hart model 100 goniometer) coupled with a high-resolution CMOScamera (e.g., 6˜60× magnification, Thor Laboratories). For each WCAmeasurement, about 4 μL volume of water is dropped to form a still waterdroplet on the specimen surface, and its optical shadowgraph is obtainedusing the CMOS camera, as shown in FIG. 1. The optical shadowgraph isquantitatively analyzed using ImageJ software to determine the WCA foreach measurement. Multiple WCA measurements are performed at variouslocations inside each specimen surface, and an average value ofmeasurement results is obtained.

In other embodiments, at least one portion of the first major surfacecomprising the reaction product of the surface modifier has a spectralreflectance of less than about 35%; less than about 30%; less than about25%; less than about 20%; less than about 15%; less than about 10%; orless than about 5% within the visible spectrum (e.g., 400 nm to about700 nm). In some embodiments, at least one portion of the first majorsurface comprising the reaction product of the surface modifier has aspectral reflectance of about 1% to about 35%; about 1% to about 25%;about 10% to about 25%; about 5% to about 30%; about 5% to about 20%;about 5% to about 15%; or about 1% to about 5% within the visiblespectrum.

The spectral reflectance within the visible spectrum for the at leastone portion of the first major surface can be measured in any suitableway. One method for measuring the spectral reflectance for the at leastone portion of the first major surface involves using a UV-VIS-NIRspectrometer (e.g., USB4000 & Flame NIR, Ocean Optics Co.) with normalincidence, as schematically illustrated in FIG. 2. Reflectance of thesurface is its effectiveness in reflecting radiant energy and defined asthe fraction of incident electromagnetic power that is reflected by thesurface. The most general definition for reflectance ρ is the ratio ofthe radiant flux reflected ϕ_(r) to the incident radiant flux ϕ_(i), or

$\begin{matrix}{\rho = \frac{\Phi_{r}}{\Phi_{i}}} & (1)\end{matrix}$

Spectral reflectance is similarly defined at a specified wavelength λ as

$\begin{matrix}{{\rho (\lambda)} = \frac{\Phi_{\lambda \; r}}{\Phi_{\lambda \; i}}} & (2)\end{matrix}$

The UV-VIS-NIR spectrometer measures the reflectance of the specimensurface in the wavelength range of about 450 nm to about 1670 nm. Anintegrating sphere is connected to the spectrometer for reflectance datacollection. Before reflectance measurement, calibration of thereflectance scale is performed by measuring the incident flux remainingin the sphere after reflecting from a standard reference material. Thenthe specimen is placed against the entrance port for the actualreflectance measurement. OCEANVIEW® software was utilized to process andvisualize the spectral reflectance measurement results. Each specimensurface is measured for multiple (e.g., four) times at variouslocations, and the averaged spectral reflectance is assessed.

In some embodiments, in addition to the WCA and reflectance describedherein, the at least one portion of the first major surface has aspectral reflectance of less than about 60%; less than about 55%; lessthan about 50%; less than about 45%; less than about 40%; less thanabout 30%; less than about 35%; less than about 30%; less than about25%; less than about 20%; less than about 15%; less than about 10%; orless than about 5% within the IR-A spectrum (e.g., 700 nm to 1400 nm).In other embodiments, in addition to the WCA and reflectance describedherein, the at least one portion of the first major surface has aspectral reflectance of about 1% to about 60%; about 5% to about 35%;about 1% to about 5%; about 20% to about 50%; about 20% to about 35%;about 15% to about 35%; about 40% to about 60%; or about 25% to about35% within the IR-A spectrum.

In some embodiments, in addition to the WCA and reflectance describedherein, the at least one portion of the first major surface has aspectral reflectance of less than about 60%; less than about 55%; lessthan about 50%; less than about 45%; less than about 40%; less thanabout 30%; less than about 35%; less than about 30%; less than about25%; less than about 20%; less than about 15%; less than about 10%; orless than about 5% within the IR-B spectrum (e.g., 1400 nm to 3000 nm).In other embodiments, the at least one portion of the first majorsurface has a spectral reflectance of about 1% to about 60%; about 5% toabout 35%; about 1% to about 5%; about 20% to about 50%; about 20% toabout 35%; about 15% to about 35%; about 40% to about 60%; or about 25%to about 35% within the IR-B spectrum.

In some embodiments, in addition to the WCA and reflectance describedherein and the spectral reflectance within the IR-A spectrum, the atleast one portion of the first major surface has a spectral reflectanceof less than about 60%; less than about 55%; less than about 50%; lessthan about 45%; less than about 40%; less than about 30%; less thanabout 35%; less than about 30%; less than about 25%; less than about20%; less than about 15%; less than about 10%; or less than about 5%within the IR-B spectrum. In other embodiments, in addition to the WCAand reflectance described herein and the spectral reflectance within theIR-A spectrum, the at least one portion of the first major surface has aspectral reflectance of about 1% to about 60%; about 5% to about 35%;about 1% to about 5%; about 20% to about 50%; about 20% to about 35%;about 15% to about 35%; about 40% to about 60%; or about 25% to about35% within the IR-B spectrum.

In some embodiments, the modified metal piece is made of any suitablemetal including steel, titanium, aluminum, magnesium, and alloysthereof. Specific examples of suitable materials for the modified metalpiece include, but are not limited to, AISI 4130 steel, titaniumTi-6Al-4V alloy (Ti-6Al-4V), aluminum alloy 6061 alloy (AA-6061) ormagnesium AZ31B alloy (Mg AZ31B).

The modified metal piece of the various embodiments described herein canbe made of aluminum alloys. Aluminum alloys can be categorized into anumber of groups based on the particular material's characteristics suchas its ability to respond to thermal and mechanical treatment and theprimary alloying element added to the aluminum alloy. Wrought and castaluminums have different systems of identification. The wrought systemis a 4-digit system and the castings having a 3-digit and 1-decimalplace system. In some embodiments, wrought aluminum alloys arecontemplated, including the 1000-, 2000-, 3000-, 4000-, 5000-, 6000-,and 7000-series of wrought aluminum alloys which can be categorized asshown in Table 1, where: x, if different from 0, indicates amodification of the specific alloy, and y and z are arbitrary numbersgiven to identify a specific alloy in the series. For example,5000-series alloy 5183, the number 5 indicates that it is of themagnesium alloy series, the 1 indicates that it is the 1st modificationto the original alloy 5083, and the 83 identifies it in the 5xyz series.The only exception to this alloy numbering system is with the 1xyzseries aluminum alloys (pure aluminums) in which case, y and z providethe minimum aluminum percentage above 99%. Thus, for example,1000-series alloy 1350 comprises 99.50% minimum aluminum.

TABLE 1 Alloy Series Principal Alloying Element 1xyz 99.000% aluminum2xyz Copper 3xyz Manganese 4xyz Silicon 5xyz Magnesium 6xyz Magnesiumand silicon 7xyz Zinc

As discussed herein, at least one portion of the first major surfacecomprises the reaction product of a surface modifier. In someembodiments, the surface modifier is a silane of the formula (I):

X¹ ₃SiR¹  (I)

wherein each X¹ is halogen or a C₁-C₆-alkoxy group; and R¹ is aC₈-C₂₀-fluoro-substituted alkyl group.

The terms “halo,” “halogen,” or “halide” group, as used herein, bythemselves or as part of another substituent, mean, unless otherwisestated, a fluorine, chlorine, bromine, or iodine atom. In someembodiments X¹ is chlorine.

The term “alkoxy” as used herein refers to an “—O-alkyl” or “—O—cycloalkyl” group. The term “alkyl,” as used herein refers tosubstituted or unsubstituted straight chain and branched alkyl groupsand cycloalkyl groups having from 1 to 40 carbon atoms (C₁-C₄₀), 1 toabout 20 carbon atoms (C₁-C₂₀), 1 to 12 carbons (C₁-C₁₂), 1 to 8 carbonatoms (C₁-C₈), or, in some embodiments, from 1 to 6 carbon atoms(C₁-C₆). Examples of straight chain alkyl groups include those with from1 to 8 carbon atoms such as methyl, ethyl, n-propyl, n-butyl, n-pentyl,n-hexyl, n-heptyl, and n-octyl groups. Examples of branched alkyl groupsinclude, but are not limited to, isopropyl, iso-butyl, sec-butyl,t-butyl, neopentyl, isopentyl, and 2,2-dimethylpropyl groups.Representative substituted alkyl groups can be substituted one or moretimes with any of the organofunctional groups listed herein, forexample, amino, hydroxy, cyano, carboxy, nitro, thio, alkoxy, andhalogen groups.

The term “cycloalkyl” as used herein refers to substituted orunsubstituted cyclic alkyl groups such as, but not limited to,cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, andcyclooctyl groups. In some embodiments, the cycloalkyl group can have 3to about 8-12 ring members, whereas in other embodiments the number ofring carbon atoms range from 3 to 4, 5, 6, or 7. In some embodiments,cycloalkyl groups can have 3 to 6 carbon atoms (C₃-C₆). Cycloalkylgroups further include polycyclic cycloalkyl groups such as, but notlimited to, norbornyl, adamantyl, bornyl, camphenyl, isocamphenyl, andcarenyl groups, and fused rings such as, but not limited to, decalinyl,and the like. Representative substituted cycloalkyl groups can besubstituted one or more times with any of the organofunctional groupslisted herein, for example, amino, hydroxy, cyano, carboxy, nitro, thio,alkoxy, and halogen groups.

In some embodiments, R¹ is a group having the formulaC_(n)—F_(2n+1)—(CH₂)₂-(organofunctional group), wherein the“organofunctional group” is 1H, 1H, 2H, 2H-perfluoralkyl; and n is aninteger from 8 to 20.

As discussed herein, the at least one portion of the first major surfacecomprises the reaction product of a surface modifier. The reactionproduct results from a reaction between the at least one portion of thefirst major surface that has been exposed to nanosecond laser-basedhigh-throughput surface nanostructuring (nHSN) and the surface modifier.While not wishing to be bound by any specific theory, it is believedthat the reaction between the surface modifier (e.g., a silane of theformula (I)) and the at least one portion of the first major surfacethat has been exposed to nHSN can be described by two mechanisms: (1)etching, or (2) surface fluorination. Scanning electron micrographs ofat least one portion of the first major surface that has been exposed tonHSN shows the formation of nanostructures that could be the result ofetching of the at least one portion of the first major surface that hasbeen exposed to nHSN. But there are also chemical analyses that havebeen performed, whose results are probative of surface fluorination. Andone cannot rule out that it could be a combination of etching andsurface fluorination. Regardless of which mechanism(s) is (are)opertative, the surface modifier somehow reacts with the at least oneportion of the first major surface that has been exposed to nHSN to givea reaction product that appears to be covalently bound to the at leastone portion of the first major surface.

As described herein, the at least one portion of the first major surfacehas a random micro- and nanoscale structure. In contrast, existinglaser-based surface texturing methods often use ultrashort pulse lasers(e.g., femtosecond or picosecond pulse lasers) generate ordered orperiodic micro-/nano-scale features. For example, existing laser-basedtexturing methods create patterns of microscale trenches, while otherscreate laser-induced periodic surface structure (LIPSS), which isperiodic at the nanoscale. See, e.g., SEM micrographs shown in FIG. 3.But none of the existing laser-based texturing methods create randommicro- and nanoscale structure, such as that shown in FIG. 4.

FIG. 4 is scanning electron microscope (SEM) micrographs of various AISI4130 steel specimens. The specimens processed by nHSN and water-confinednanosecond laser texturing (wNLT) used the same laser power intensity of7.3 GW/cm². Micrographs of untreated raw specimen show a horizontal laypattern at various magnifications from 100× to 20,000×. The wNLT, whichhas not been treated with a surface modifying agent, shows themicroscale ripples induced from the nanosecond laser-steel interactionunder water confinement. The nHSN specimen shows an isotropic texturewith numerous tiny pores homogenously distributed at 100×˜2,000×magnifications. But viewed under 20,000×˜50,000× magnifications, thenHSN specimen is characterized of numerous structures of various randomshapes of rods, cones and cavities. These features vary in size rangingfrom less than 100 nm to several hundreds of nm.

The surface modified metal piece(s) described herein can be made by aprocess comprising: immersing a metal piece having a first major surfacein an aqueous medium; texturing at least a portion of the first majorsurface along a nanosecond laser scan path at a laser scanning time ofat least about 0.25 seconds/in² to obtain a textured metal piece havinga textured surface along the scan path; removing the textured metalpiece from the aqueous medium; and immersing the textured metal piece ina solution comprising a surface modifier, wherein the surface modifierreacts with the textured surface to obtain a modified metal surface;wherein: at least one of the textured surface along the scan path andthe textured surface that reacts with the surface modifier has a randommicro- and nanoscale structure; the nanosecond laser emits pulses of anappropriate energy onto the first major surface along the scan path; thenanosecond laser has a laser power intensity of greater than about 0.2GW/cm²; the surface modifier reacts substantially only with the texturedsurface along the scan path; and the textured surface along the scanpath that reacts with the surface modifier has at least one of a watercontact angle when exposed to water of at least 120° and a spectralreflectance of less than 25% within the visible spectrum.

As described herein, the laser scanning time can be at least about 0.25seconds/in², but can be significantly faster at, e.g., at least about0.1 seconds/in²; at least about 0.05 seconds/in²; at least about 0.025seconds/in²; from about 0.025 seconds/in² to about 15 seconds/in²; about0.025 seconds/in² to about 0.25 seconds/in²; about 0.1 seconds/in² toabout 0.9 seconds/in²; or about 1 seconds/in² to about 5 seconds/in².

As used herein, the term “appropriate energy” generally refers to ananosecond laser pulse of from about 300 mJ to about 20 J; about 300 mJto about 800 mJ; about 300 mJ to about 2 J; about 300 mJ to about 1 J;about 500 mJ to about 1 J; about 500 mJ to about 1.5 J; about 500 mJ toabout 800 mJ; or about 450 mJ to about 900 mJ.

As described herein, the laser intensity can be greater than about 0.2GW/cm² and can be greater than about 0.5 GW/cm²; greater than about 1GW/cm²; greater than about 1.5 GW/cm²; greater than about 2 GW/cm²;greater than about 5 GW/cm²; greater than about 10 GW/cm²; greater thanabout 15 GW/cm²; greater than about 20 GW/cm²; about 0.2 GW/cm² to about20 GW/cm²; about 0.2 GW/cm² to about 5 GW/cm²; about 5 GW/cm² to about15 GW/cm²; or about 10 GW/cm² to about 20 GW/cm².

Embodiments described herein also relate to a method of making a surfacemodified metal piece, the method comprising: immersing a metal piecehaving a first major surface in an aqueous medium; texturing at least aportion of the first major surface along a nanosecond laser scan path ata laser scanning time of at least about 0.25 seconds/in² to obtain atextured metal piece having a textured surface along the scan path;removing the textured metal piece from the aqueous medium; and immersingthe textured metal piece in a solution comprising a surface modifier,wherein the surface modifier reacts with the textured surface to obtaina modified metal surface; wherein: at least one of the textured surfacealong the scan path and the textured surface that reacts with thesurface modifier has a random micro- and nanoscale structure; thenanosecond laser emits pulses of an appropriate energy onto the firstmajor surface along the scan path; the nanosecond laser has a laserpower intensity of greater than about 0.2 GW/cm²; the surface modifierreacts substantially only with the textured surface along the scan path;and the textured surface along the scan path that reacts with thesurface modifier has at least one of a water contact angle when exposedto water of at least 120° and a spectral reflectance of less than 25%within the visible spectrum.

As used herein, the term “aqueous medium” generally refers to a mediumcomprising water but can include a medium comprising 50% or more waterand a water miscible solvent such as an alkanol (e.g., methanol orethanol), acetonitrile, acetone, ethyl acetate, and the like andmixtures thereof. In some embodiments, the aqueous medium is comprisedof 100% water.

The solution comprising the surface modifier can comprise the surfacemodifier in a suitable solvent. Suitable solvents include, but are notlimited to, alkanols (e.g., methanol or ethanol), acetone, and ethyleneglycol.

The surface modified metal pieces of the various embodiments describedherein have various applications where the surface, so modified, resisticing, reduce drag, are self-cleaning, are anti-biofouling, resistcorrosion, and have low spectral reflectance of visible, IR-A, and/orIR-B radiation.

Anti-icing on the metal structural surface has long been a technologicalchallenge for aviation, space flight, and for radar devices. The methodsof making a surface modified metal piece according to the disclosure canprovide, among other things, a superhydrophobic metal surface to addresssuch a challenge. Water droplets can roll off the cold superhydrophobicsurface quickly without freezing. In contrast, drops on an untreatedsurface spread quickly and form a thin film on the surface that canfreeze immediately.

The methods of making a surface modified metal piece according to thedisclosure can provide metal surfaces on marine vehicles that are, amongother things, superhydrophobic so as to reduce the frictional drag andsave in energy consumption. This drag-reduction property provides asignificant potential for energy-savings in applications ranging frompropulsion of marine vessels to transporting liquids through conduits.

The methods of making a surface modified metal piece according to thedisclosure can provide metal surfaces that are, among other things,superhydrophobic so as to facilitate the de-wetting of the surface andenable water droplets to roll off easily, taking away the dirt and otherpollutants.

The methods of making a surface modified metal piece according to thedisclosure can provide metal surfaces that are, among other things,superhydrophobic so as to enhance anti-biofouling capability.

The methods of making a surface modified metal piece according to thedisclosure can provide metal surfaces that are, among other things,superhydrophobic so as to repel water and prevent the metal surface frombecoming corroded.

The methods of making a surface modified metal piece according to thedisclosure can provide metal surfaces that are, among other things,highly absorptive so as to have low spectral reflectance of visible,IR-A, and/or IR-B radiation. Such surfaces would be particularly usefulin optical packaging, thermal detection, and telescopes.

Values expressed in a range format should be interpreted in a flexiblemanner to include not only the numerical values explicitly recited asthe limits of the range, but also to include all the individualnumerical values or sub-ranges encompassed within that range as if eachnumerical value and sub-range were explicitly recited. For example, arange of “about 0.1% to about 5%” or “about 0.1% to 5%” should beinterpreted to include not just about 0.1% to about 5%, but also theindividual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g.,0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range.The statement “about X to Y” has the same meaning as “about X to aboutY,” unless indicated otherwise. Likewise, the statement “about X, Y, orabout Z” has the same meaning as “about X, about Y, or about Z,” unlessindicated otherwise.

In this document, the terms “a,” “an,” or “the” are used to include oneor more than one unless the context clearly dictates otherwise. The term“or” is used to refer to a nonexclusive “or” unless otherwise indicated.In addition, it is to be understood that the phraseology or terminologyemployed herein, and not otherwise defined, is for the purpose ofdescription only and not of limitation. Any use of section headings isintended to aid reading of the document and is not to be interpreted aslimiting. Further, information that is relevant to a section heading mayoccur within or outside of that particular section. Furthermore, allpublications, patents, and patent documents referred to in this documentare incorporated by reference herein in their entirety, as thoughindividually incorporated by reference.

In the methods described herein, the steps can be carried out in anyorder without departing from the principles of the invention, exceptwhen a temporal or operational sequence is explicitly recited.Furthermore, specified steps can be carried out concurrently unlessexplicit claim language recites that they be carried out separately. Forexample, a claimed step of doing X and a claimed step of doing Y can beconducted simultaneously within a single operation, and the resultingprocess will fall within the literal scope of the claimed process.

The term “about” as used herein can allow for a degree of variability ina value or range, for example, within 10%, within 5%, or within 1% of astated value or of a stated limit of a range.

EXAMPLES

The present invention can be better understood by reference to thefollowing examples which are offered by way of illustration. The presentinvention is not limited to the examples given herein.

Example 1

The nanosecond laser-based high-throughput surface nanostructuring(nHSN) process comprises two steps: (1) a high energy nanosecond pulselaser scans the material surface contained under water using a largespatial increment and a fast processing speed; and (2) the lasertextured surface is further chemically treated. See FIG. 5.

The first step of the process is referred to herein as water-confinednanosecond laser texturing (wNLT). The experimental setup for the wNLTuses a Q-Switched Nd:YAG nanosecond laser (Spectra-Physics Quanta-RayLab-150, wavelength 1064 nm) with a high energy per pulse on the orderof several hundreds of mJ/pulse. During the wNLT process, the laserrepetition rate is 10 pulses per second with a laser pulse duration of 6to 8 ns. A galvanometer laser scanner (SCANLAB intelliSCAN® 20)furnished with an f-theta objective with a focal length of 255 mmdirects the laser to texture the top surface of the specimen. A dynamicfocusing unit (SCANLAB varioSCAN_(de) 40i) is integrated with thescanner and provides a dynamic precise positioning of the laser focusalong the optical z axis, thus enabling three-dimensional (3D) scanningalong the contours of the workpiece being processed. See, e.g., FIG. 6.The specimen is submerged in deionized water during the wNLT step, whichconfines the laser pulse-induced plasma and enhances the texturingeffect.

During the second, CIT step, the laser-textured work material isimmersed in an ethanol solution with 1.5% volume percentage silanereagent (e.g., Trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane, 97%) atroom temperature for about 3 hours. Specimens are then cleaned and driedat 80° C. in a vacuum oven for 1 hour.

FIG. 7 is a schematic representation of a wNLT system and its opticalpath used for the current invention. The workpiece is kept underdeionized water confinement (around 8 mm depth from the specimensurface) in a tank, which is positioned using computer-controlledstages. The combination of laser scan head and computer-controlledstages allows to have a wide range of laser scanning area during theprocess. Both laser and scan head are controlled by a microcontrollerfor scanning along a pre-designed path. The scan head is also connectedto a water cooling system to avoid any undesirable heating during theprocess.

FIG. 6 shows a laser scanning path that can be used for wNLT. The laserscan head scans the top surface of the work material in a “zig-zag”pattern. The X-spacing (or pitch) defines the distance between twosequential laser scan lines and is preset through computer control. TheLaser Scan Line Density, as determined by Eq. 3, defines how many laserscan lines are required to scan a 1-inch width area. The Y-spacingbetween two sequential laser shots along the scanning direction isdetermined by the Laser Repetition Rate and preset Laser Scanning Speedas in Eq. 4. The Overlap Ratio is set by the ratio of Overlap Area tothe Laser Spot Area as in Eq. 5. For all the experimental conditions inthis study, a same value was applied for both X-spacing and Y-spacing,which guarantees the same Overlap Ratio of 50% in both directions. TheSpecific Laser Scanning Time (min/in²) defines the time needed to scan aunit area of square inch as shown in Eq. 6. Laser Processing Ratedefines the scanning area per unit time as shown in Eq. 7. The LaserPulse Energy (mJ) of the Q-Switched Nd:YAG nanosecond laser(Spectra-Physics Quanta-Ray Lab-150, wavelength 1064 nm) can beadjustable from 0 to 710 mJ per pulse. The Laser Spot Area can beadjusted by moving the Z stage away from the focal plane. The LaserPower Intensity and Laser Fluence can be calculated using Eqs. 8-9,respectively.

For example, a specific laser scanning time of 15 s/in² (or 0.25min/in²) was achieved for wNLT of AISI 4130 Steel using the followingprocess parameters: Laser Power Intensity of 0.20 GW/cm², Pulse Energyof 338 mJ, Laser Spot Diameter of 5.2 mm, Y-spacing of 2.1 mm, LaserScan Line Density of 12 lines/in, Overlap Ratio of 50%, and LaserScanning Speed of 21 mm/s.

$\begin{matrix}{\mspace{79mu} {{{Laser}\mspace{14mu} {Scan}\mspace{14mu} {Line}\mspace{14mu} {Density}\mspace{14mu} \left( {{lines}\text{/}{in}} \right)} = \frac{1\mspace{14mu} {in}}{X\text{-}{spacing}}}} & (1) \\{\mspace{79mu} {{Y\text{-}{spacing}} = \frac{{Laser}\mspace{14mu} {Scanning}\mspace{14mu} {Speed}}{{Laser}\mspace{14mu} {Repetition}\mspace{14mu} {Rate}}}} & (2) \\{\mspace{79mu} {{{Overlap}\mspace{14mu} {Ratio}} = {\frac{{Overlap}\mspace{14mu} {Area}}{{Laser}\mspace{14mu} {Spot}\mspace{14mu} {Area}} \times 100\%}}} & (3) \\{{{Specific}\mspace{14mu} {Laser}\mspace{14mu} {Scanning}\mspace{14mu} {Time}} = {\frac{1\mspace{14mu} {in}}{{Laser}\mspace{14mu} {Scanning}\mspace{14mu} {Speed}} \times {Laser}\mspace{14mu} {Scan}\mspace{14mu} {Line}\mspace{14mu} {Density}}} & (4) \\{{{Laser}\mspace{14mu} {Processing}\mspace{14mu} {Rate}\mspace{14mu} \left( {{in}^{2}\text{/}\min} \right)} = \frac{1}{{Specific}\mspace{14mu} {Laser}\mspace{14mu} {Scanning}\mspace{14mu} {Time}}} & (5) \\{{{Laser}\mspace{14mu} {Power}\mspace{14mu} {Intensity}\mspace{14mu} \left( {{GW}\text{/}{cm}^{2}} \right)} = \frac{{Pulse}\mspace{14mu} {Energy}}{{Pulse}\mspace{14mu} {Duration} \times {Laser}\mspace{14mu} {Spot}\mspace{14mu} {Area}}} & (6) \\{\mspace{79mu} {{{Laser}\mspace{14mu} {Fluence}\mspace{14mu} \left( {J\text{/}{cm}^{2}} \right)} = \frac{{Pulse}\mspace{14mu} {Energy}}{{Laser}\mspace{14mu} {Spot}\mspace{14mu} {Area}}}} & (7)\end{matrix}$

Based on surface testing results, the methods/processes described hereinproduce superhydrophobic and anti-reflective surfaces for multipleimportant engineering metal alloys including AISI 4130 Steel, TitaniumTi-6Al-4V alloy (Ti-6Al-4V), and Aluminum Alloy 6061 alloy (AA-6061),magnesium AZ31B alloy (Mg AZ31B).

The surface structures produced by the methods/processes describedherein are random nanostructures of various protrusions and cavities ofsize ranging from less than 100 nm to several hundreds of nm randomlydistributed in the treated area. Viewed at a meso- or macro-scale,surfaces processed by the methods/processes described herein have anisotropic texture with numerous tiny pores homogenously distributed inthe treated area. These random nanostructures are produced in a top-downapproach during the methods/processes described herein.

The existing laser-based surface texturing technologies, in order toachieve superhydrophobic and anti-reflective metal surfaces, produceordered microscale structures, either ordered microgrooves or microscalelaser-induced periodic surface structure (LIPSS).

The relationship between the laser process parameters and the resultantsurface wettability appears to be material-dependent and has beenestablished as follows:

For AISI 4130 Steel, the methods/processes described herein produceconsistent superhydrophobic surfaces, as long as the laser powerintensity is equal or greater than 0.2 GW/cm². Using a laser powerintensity less than 0.2 GW/cm², the treated surface does not achievesuperhydrophobic with a contact angle less than 150°.

For AA 6061, the methods/processes described herein produce consistentsuperhydrophobic surfaces, as long as the laser power intensity is equalor greater than 0.4 GW/cm². Using a laser power intensity less than 0.4GW/cm², the treated surface does not achieve superhydrophobic with acontact angle less than 150°.

For Mg AZ31B, the methods/processes described herein produce consistentsuperhydrophobic surfaces, as long as the laser power intensity is equalor greater than 0.6 GW/cm²

For Ti-6Al-4V, the methods/processes described herein produce consistenthydrophobic surfaces with WCA ranging from 120° to 135° using a laserpower intensity of 0.6-8.4 GW/cm².

The relationship between the laser process parameters and the resultantsurface spectral reflectance within the visible and infrared spectrumsappears to be material-dependent and has been established as follows.

For AISI 4130 Steel, using a laser power intensity from 0.6 to 1.3GW/cm², the methods/processes described herein reduced the spectralreflectance to 20% within the visible spectrum, 20%-25% within the IR-Aspectrum, 25%-35% within the IR-B spectrum. Using a laser powerintensity from 2.4 to 8.4 GW/cm², the methods/processes described hereinsignificantly reduced the spectral reflectance to 8.5%˜9.3% within thevisible spectrum, 9.3%-13.7% within the IR-A spectrum, 13.7%-17.7%within the IR-B spectrum. Using a laser power intensity of 18.2 GW/cm²,the methods/processes described herein further reduced the spectralreflectance to 3%˜5% within the visible spectrum, 5%-8% within the IR-Aspectrum, 8%-11% within the IR-B spectrum.

For Ti-6Al-4V, using a laser power intensity from 0.6 to 0.9 GW/cm², themethods/processes described herein reduced the spectral reflectance to6%˜8% within the visible spectrum, 8%-17% within the IR-A spectrum,17%-22% within the IR-B spectrum. Using a laser power intensity from 1.3to 8.4 GW/cm², the methods/processes described herein significantlyreduced the spectral reflectance to 6%˜8% within the visible spectrum,6%-10% within the IR-A spectrum, 10%-14% within the IR-B spectrum.

For AA 6061, using a laser power intensity from 0.6 to 8.4 GW/cm², themethods/processes described herein significantly reduced the spectralreflectance to 24%˜31% within the visible spectrum, 24%-55% within theIR-A spectrum, 48%-55% within the IR-B spectrum.

Example 2

The wettability of the specimen surface produced by themethods/processes described herein was experimentally evaluated throughwater wetting tests. The definition of surface wettability can bedescribed as follows: a surface is said to be wetted if one type ofliquid spreads over the surface evenly without the formation ofdroplets. When the liquid is water, it spreads over the hydrophilicsurface without the formation of droplets; while water droplets willform on hydrophobic surfaces. Hydrophobicity and hydrophilicity arerelative terms. A simple quantitative method for defining the relativedegree of interaction of water with a solid surface is the water contactangle (WCA) of a water droplet on a solid substrate. WCA is defined asthe angle, conventionally measured through the water droplet, where awater-vapor interface meets a solid surface and can be used to quantifythe wettability of a solid surface.

The surface wettability to water can be categorized into four kinds:hydrophobic, hydrophilic, superhydrophobic and superhydrophilic. If WCAis less than 30°, the surface is designated hydrophilic. If waterspreads over a surface and the contact angle at the spreading front edgeof the water is less than 10°, the surface is often designated assuperhydrophilic (provided that the surface is not absorbing the water,dissolving in the water or reacting with the water). On a hydrophobicsurface, water forms distinct droplets. As the hydrophobicity increases,the contact angle of the droplets with the surface increases. Surfaceswith WCA greater than 90° are designated as hydrophobic. When WCA isgreater than 150°, the surface is generally regarded assuperhydrophobic.

Water Contact Angle for the treated specimen surface was measured duringthe wettability test using a contact angle goniometer (Rame-Hart model100) coupled with a high-resolution CMOS camera (6˜60× magnification,Thor Laboratories). For each WCA measurement, about 4 μL volume of waterwas dropped to form a still water droplet on the specimen surface, andits optical shadowgraph was obtained using the CMOS camera, as shown inFIG. 1. The optical shadowgraph was quantitatively analyzed using opensource ImageJ software to determine the WCA for each measurement.Multiple WCA measurements were performed at various locations insideeach specimen surface, and the average value of measurement results wasobtained. Various materials produced by the methods/processes describedherein were evaluated in these wetting tests including AISI 4130 Steel,Titanium Ti-6Al-4V alloy (Ti-6Al-4V), and Aluminum Alloy 6061 alloy(AA-6061), Magnesium AZ31B alloy (Mg AZ31B).

FIG. 8 shows the sprayed water droplets formed on the AA-6061 specimensurface treated by the methods/processes described herein. It is notedthat completely spherical water droplets form on the nHSN surface,demonstrating the superhydrophobicity. The processed area has adimension of 95 mm (length)×95 mm (width). For this specimen, a SpecificLaser Scanning Time of 29 s/in² was achieved using the following laserprocess parameters: Laser Power Intensity of 0.40 GW/cm², Pulse Energyof 338 mJ, Laser Spot Diameter of 3.7 mm, Y-spacing of 1.5 mm, LaserScan Line Density of 17 lines/in. Overlap Ratio of 50%, and LaserScanning Speed of 15 mm/s. It took 6.7 minutes to scan this 95 mm×95 mmarea. It should be noted the Laser Processing Rate is still limited inthis case due to the laser equipment constraint of the current systemusing the Spectra-Physics Quanta-Ray Lab-15 nanosecond laser. Anindustry-level nanosecond laser will scale up the Laser Processing Rateand enable a larger area by using a higher Pulse Energy and a higherLaser Repetition Rate, while maintaining the same Laser Power Intensity.

The measurement results of water contact angle for AISI 4130 steelspecimens treated from various process conditions including laserablation in air, Nanosecond Laser Texturing (NLT) in air, water-confinedNanosecond Laser Texturing (wNLT), and their combinations with ChemicalImmersion Treatment (CIT). The nHSN process consists of two steps ofwNLT and CIT. The WCA was 85.8° for AISI 4130 steel specimen without anytreatment, and became 96.9° after Chemical Immersion Treatment (CIT).This indicates CIT process alone does not significantly alter thesurface wettability for specimens without laser surface treatment.Nanosecond laser ablation using the long-pulse mode (120 ns per pulseduration) produced a hydrophilic surface with a WCA less than 20°shortly after (within several hours) laser ablation. As the CIT, the WCAof the laser ablated specimen surface dramatically increased to 145°.Nanosecond Laser Texturing (NLT) in air using the Q-switch mode (6˜8 nsper pulse duration) produced a hydrophilic surface with a WCA less than20° shortly after (within several hours) laser texturing. With CIT, theWCA of the NLT specimen surface dramatically increased to 131°.Water-confined Nanosecond Laser Texturing (wNLT) using the Q-switch mode(6˜8 ns per pulse duration) produced a hydrophilic surface with a WCAless than 20° shortly after (within several hours) laser texturing.However, by a following step of CIT after wNLT, the WCA of the nHSNspecimen surface dramatically increased to 161°. Both NLT in air andnanosecond laser ablation processes require a fine spatial resolution,e.g., a fine laser line spacing of 60˜100 μm, to scan the overallspecimen surface, which leads to a low throughput for surfaceprocessing. In addition, these nanosecond laser processing conditionsdid not produce superhydrophobic surface with WCA greater than 150°. Themethods/processes described herein produce superhydrophobic surface withWCA greater than 150°. The wNLT step significantly improves theprocessing efficiency by performing nanosecond laser texturing underwater confinement. The wNLT step uses a large laser line spacing, e.g.,2.1 mm for a 5.2 mm laser spot, and a fast processing speed, e.g., 21mm/s, and hence significantly increases the Specific Laser Scanning Timefrom hundreds of minutes per square inch to 15 s/in². In addition, thenHSN process enables large area processing for practical throughput.

Example 3

Water contact angle measurement results for AISI 4130 steel specimensproduced by the methods/processes described herein using various laserpower intensities ranging from 0.1 to 18.2 GW/cm². The uncertainty wastypically around ±2° for each test. The measurement for 0 GW/cm² wasperformed on the specimens produced by the CIT treatment alone, andtheir results show a WCA of 96.9°. The specimens treated by low laserpower intensities from 0.1 to 0.15 GW/cm² during the wNLT step showedimproved hydrophobicity with increased WCAs up to 139.4°. These testsalso indicate that a higher laser power intensity during the wNLT stephelp increase the WCA by the nHSN process. The specimens treated bylaser power intensities from 0.2 to 18.2 GW/cm² during the nHSN processall achieve superhydrophobicity with WCA greater than 150°. Varyinglaser power intensity does not significantly alter the WCA for thesesuperhydrophobic AISI 4130 steel specimens. These results indicate awide laser operation window exists for the nHSN process to produceconsistent superhydrophobic AISI 4130 steel surfaces, as long as thelaser power intensity is equal or greater than 0.2 GW/cm².

Example 4

Water contact angle measurement results for AA-6061 specimens producedby the methods/processes described herein using various laser powerintensities ranging from 0.2 to 8.4 GW/cm². Similarly, the uncertaintywas typically around ±2° for each test. The specimens treated by lowlaser power intensities from 0.2 to 0.3 GW/cm² during the wNLT stepshowed improved hydrophobicity with increased WCAs up to 133.8°. Thesetests indicate that a higher laser power intensity during the wNLT stephelp increase the WCA of AA-6061 specimens processed by the nHSNprocess. The specimens treated by laser power intensities from 0.4 to8.4 GW/cm² during the nHSN process all achieve superhydrophobicity withWCA greater than 150°. Varying laser power intensity does notsignificantly alter the WCA for these superhydrophobic AA-6061specimens. These results indicate a wide laser operation window existsfor the nHSN process to produce consistent superhydrophobic AA-6061surfaces, as long as the laser power intensity is equal or greater than0.4 GW/cm².

Example 5

Water contact angle measurement results for Mg AZ31B specimens producedby the methods/processes described herein using various laser powerintensities ranging from 0.6 to 8.8 GW/cm². The uncertainty wastypically around ±2 for each test. The specimens all achievesuperhydrophobicity with WCA greater than 150°. Varying laser powerintensity does not significantly alter the WCA for thesesuperhydrophobic Mg AZ31B specimens. These results indicate a wide laseroperation window exists for the nHSN process to produce consistentsuperhydrophobic Mg AZ31B surfaces, as long as the laser power intensityis equal or greater than 0.6 GW/cm².

Water contact angle measurement results for Ti-6Al-4V specimens producedby the nHSN process using various laser power intensities ranging from0.6 to 8.4 GW/cm². The uncertainty was typically around ±2° for eachtest. The specimens all achieve hydrophobicity with WCA ranging from120° to 135°. Varying laser power intensity does not significantly alterthe WCA for these hydrophobic Ti-6Al-4V specimens.

Example 6

Water sliding tests were performed on AISI 4130 steel, AA-6061, and MgAZ31B specimens with WCA greater than 150° to further validate theirsuperhydrophobicity. Generally, water sliding angle is defined as thecritical angle where a water droplet begins to slide down an inclinedplate, which does not exceed 10° for a superhydrophobic surface. Duringthe water sliding tests, these specimens were tilted with a 6˜8° anglefrom the horizontal plane. Sliding test results showed that waterdroplet rolled off the nHSN specimen surface smoothly for all thespecimens, and thus validated their surface superhydrophobicity of thesespecimens with WCA greater than 150°. It should be noted that thecritical water sliding angle of these specimens should be less than thetilt angle of 8°. For example, a very small water sliding angle of lessthan 2° was also used for the sliding tests for AA-6061 specimens, andthe water droplet rolled off the specimen surface smoothly.

Example 7

Spectral reflectance measurement results for AISI 4130 steel specimenstreated by the methods/processes described herein using various laserpower intensities from 0.6 to 18.2 GW/cm². According to theclassification by the International Commission on Illumination (CIE),the electromagnetic spectrum between 400˜3,000 nm is subdivided intovisible spectrum from 400 nm to 700 nm, IR-A spectrum from 700 nm to1,400 nm, and IR-B spectrum from 1,400 nm to 3,000 nm. Following thisclassification, the spectrum of this reflectance measurement of 450˜1670nm is subdivided into visible spectrum from 450 nm to 700 nm, IR-Aspectrum from 700 nm to 1,400 nm, and IR-B spectrum from 1,400 nm to1,670 nm.

Spectral reflectance measurement results for untreated and mechanicallyground AISI 4130 steel specimens are also shown for comparison. Thespectral reflectance for the raw and untreated AISI 4130 steel specimensfalls 24%˜29% within the visible spectrum, 29%˜48% within the IR-Aspectrum, 48%˜54% within the IR-B spectrum. The spectral reflectance forthe mechanically ground AISI 4130 steel specimens falls 39%˜41% withinthe visible spectrum, 41%˜56% within the IR-A spectrum, 56%˜68% withinthe IR-B spectrum. Using a laser power intensity from 0.6 to 1.3 GW/cm²,the methods/processes described herein reduced the spectral reflectanceto 20% within the visible spectrum, 20%-25% within the IR-A spectrum,25%-35% within the IR-B spectrum. Using a laser power intensity from 2.4to 8.4 GW/cm², the methods/processes described herein significantlyreduced the spectral reflectance to 8.5%˜9.3% within the visiblespectrum, 9.3%-13.7% within the IR-A spectrum, 13.7%-17.7% within theIR-B spectrum. Using a laser power intensity of 18.2 GW/cm², themethods/processes described herein further reduced the spectralreflectance to 3%˜5% within the visible spectrum, 5%-8% within the IR-Aspectrum, 8%-11% within the IR-B spectrum. These results indicate that ahighly anti-reflective AISI 4130 steel surface within the visible and IRspectrum can be realized by applying the methods/processes describedherein. More importantly, the spectral reflectance of AISI 4130 steelcan be adjusted and well controlled by carefully selecting the processparameters of methods/processes described herein. The higher the laserpower intensity is applied, the lower the surface spectral reflectancewill be achieved by methods/processes described herein.

Example 8

Spectral reflectance measurement results for Ti-6Al-4V specimens treatedby the methods/processes described herein were obtained using variouslaser power intensities from 0.6 to 8.4 GW/cm². Spectral reflectancemeasurement results for untreated and mechanically ground Ti-6Al-4Vspecimens are also shown for comparison. The spectral reflectance forthe untreated and mechanically ground Ti-6Al-4V specimens falls 28%˜33%within the visible spectrum, 33%˜42% within the IR-A spectrum, 42%˜52%within the IR-B spectrum. The spectral reflectance for the mechanicallyground Ti-6Al-4V specimens falls 35%˜39% within the visible spectrum,39%˜45% within the IR-A spectrum, 45%-52% within the IR-B spectrum.Using a laser power intensity from 0.6 to 0.9 GW/cm², the nHSN processreduced the spectral reflectance to 6%˜8% within the visible spectrum,8%-17% within the IR-A spectrum, 17%-22% within the IR-B spectrum. Usinga laser power intensity from 1.3 to 8.4 GW/cm², the nHSN processsignificantly reduced the spectral reflectance to 6%˜8% within thevisible spectrum, 6%-10% within the IR-A spectrum, 10%-14% within theIR-B spectrum. These results indicate that a highly anti-reflectiveTi-6Al-4V surface within the visible and IR spectrum can be realized byapplying the nHSN treatment. More importantly, the spectral reflectanceof Ti-6Al-4V can be adjusted and well controlled by carefully selectingthe process parameters of nHSN. The higher the laser power intensity isapplied, the lower the surface spectral reflectance for Ti-6Al-4V willbe achieved by nHSN.

Example 9

Spectral reflectance measurement results for AA-6061 specimens treatedby the methods/processes described herein were obtained using variouslaser power intensities from 0.6 to 8.4 GW/cm². Spectral reflectancemeasurement results for untreated and mechanically ground AA-6061specimens are also shown for comparison. The spectral reflectance forthe untreated and mechanically ground AA-6061 specimens falls 55%˜57%within the visible spectrum, 50%˜75% within the IR-A spectrum, 75%˜85%within the IR-B spectrum. The spectral reflectance for the mechanicallyground AA-6061 specimens falls 65%˜67% within the visible spectrum,62%-80% within the IR-A spectrum, 80%-82% within the IR-B spectrum.Using a laser power intensity from 0.6 to 8.4 GW/cm², the nHSN processsignificantly reduced the spectral reflectance to 24%˜31% within thevisible spectrum, 24%-55% within the IR-A spectrum, 48%-55% within theIR-B spectrum. These results indicate that an anti-reflective AA-6061surface within the visible and IR spectrum can be realized by applyingthe nHSN treatment. It is also found that the spectral reflectance forAA-6061 does not always decrease as the laser power intensity increasingfrom 0.6 to 8.4 GW/cm².

Based on the reflectance measurement for AISI 4130 steel, AA-6061 andTi-6Al-4V specimens treated by the methods/processes described hereinproved to be a highly efficient method in reducing the reflectancewithin the visible and infrared spectra.

Example 10

Vickers microhardness measurements were performed at multiple locationsusing a 50 gf to evaluate the change in surface strength. The AISI 4130steel specimens used in these tests were by the methods/processesdescribed herein using a laser power intensity of 2.4 GW/cm². Themicrohardness of untreated specimens were 159.1±7.7 HV. Through themethods/processes described herein, the surface microhardness wasenhanced to 205.7±4.3 HV with a 29% increase. The microhardnessmeasurement results indicate that the methods/processes described hereincan enhance the surface mechanical strength and improve its resistanceto wear.

Example 11

The surface microstructures were analyzed for various specimens for viewareas ranging from 1 mm² to 4 μm² using a scanning electron microscope(SEM, model number Hitachi S-4800), as can be seen in FIG. 4. In thisstudy, the specimens processed by nHSN and wNLT used the same laserpower intensity of 7.3 GW/cm². Therefore, difference between the nHSNand wNLT surface micrographs shows any surface modification induced bythe additional CIT step of the methods/processes described herein.Providing as a baseline, the micrographs of untreated raw specimen areshown on the left of FIG. 4, and exhibits a horizontal lay pattern forthe micrographs taken at various magnifications from 100× to 20,000×. Incomparison, at 100× magnification with a view area of about 1 mm², bothnHSN and wNLT specimens show an isotropic texture without any obviouslay pattern. Apparently different from the wNLT specimen, numerous tinypores can be seen homogenously distributed over the nHSN specimen. At2,000× magnification with a view area of about 2,000 μm², the nHSNspecimen shows numerous pores of various sizes, while microscale ripplescan be seen all over the wNLT specimen surface. The microscale rippleson the wNLT specimen are induced from the nanosecond laser-steelinteraction under water confinement, which are not observed in the nHSNspecimen. This indicates the additional CIT step of themethods/processes described herein significantly modifies the surfacemorphology after the wNLT step. At 20,000× magnification with a viewarea of about 20 μm², structures of various shapes of protrusions andpores are revealed on the nHSN specimen, while the wNLT specimen isstill characterized with microscale ripples decorated with some cracksand pores. At 50,000× magnification with a view area of about 4 μm², itis clearly discovered that the nHSN specimen is characterized ofnumerous random structures of rods, cones, platelets and pores. Thesefeatures vary in size ranging from less than 100 nm to several hundredsof nm. In contrast, the wNLT specimen within such a small view area ischaracterized as a flat area dispersed with multiple nanoscale pores.

The present invention provides for the following embodiments, thenumbering of which is not to be construed as designating levels ofimportance:

Embodiment 1 relates to a surface modified metal piece comprising: afirst major surface, wherein at least one portion of the first majorsurface: comprises the reaction product of a surface modifier; has arandom micro- and nanoscale structure; and has at least one of a watercontact angle when exposed to water of at least about 120° and aspectral reflectance of less than about 25% within the visible spectrum.

Embodiment 2 relates to the surface modified metal piece of Embodiment1, wherein the at least one portion of the first major surfacecomprising the surface modifier has a water contact angle when exposedto water of at least 150°.

Embodiment 3 relates to the surface modified metal piece of Embodiments1-2, wherein the metal piece is made of steel, titanium, aluminum,magnesium, and alloys thereof.

Embodiments 4 relates to the surface modified metal piece of Embodiments1-3, wherein the metal piece is AISI 4130 steel, titanium Ti-6Al-4Valloy (Ti-6Al-4V), aluminum alloy 6061 alloy (AA-6061) or magnesiumAZ31B alloy (Mg AZ31B).

Embodiment 5 relates to the surface modified metal piece of Embodiments1-4, wherein the surface modifier is the reaction product of a silane ofthe formula:

X¹ ₃SiR¹

wherein each X¹ is halogen or a C₁-C₆-alkoxy group; and R¹ is aC₈-C₂₀-fluoro-substituted alkyl group; and reactive sites on a majorsurface of the metal piece.

Embodiment 6 relates to the surface modified metal piece of Embodiment5, wherein R¹ is a group having the formulaC_(n)—F_(2n+1)—(CH₂)₂-(organofunctional group), wherein theorganofunctional group is 1H, 2H, 2H-perfluoralkyl; and n is an integerfrom 8 to 20.

Embodiment 7 relates to the surface modified metal piece of Embodiments1-6, wherein the at least one portion of the first major surface has aspectral reflectance of less than 60% within the IR-A spectrum.

Embodiment 8 relates to the surface modified metal piece of Embodiments1-7, wherein the at least one portion of the first major surface has aspectral reflectance of less than 30% within the IR-A spectrum.

Embodiment 9 relates to the surface modified metal piece of Embodiments1-8, wherein the at least one portion of the first major surface has aspectral reflectance of less than 60% within the IR-B spectrum.

Embodiment 10 relates to the surface modified metal piece of embodiments1-9, wherein the at least one portion of the first major surface has aspectral reflectance of less than 40% within the IR-B spectrum.

Embodiment 11 relates to a surface modified metal piece made by theprocess comprising: immersing a metal piece having a first major surfacein an aqueous medium; texturing at least a portion of the first majorsurface along a nanosecond laser scan path at a laser scanning time ofat least about 0.25 seconds/in2 to obtain a textured metal piece havinga textured surface along the scan path; removing the textured metalpiece from the aqueous medium; and immersing the textured metal piece ina solution comprising a surface modifier, wherein the surface modifierreacts with the textured surface to obtain a modified metal surface;wherein: at least one of the textured surface along the scan path andthe textured surface that reacts with the surface modifier has a randommicro- and nanoscale structure; the nanosecond laser emits pulses of anappropriate energy onto the first major surface along the scan path; thenanosecond laser has a laser power intensity of greater than about 0.2GW/cm²; the surface modifier reacts substantially only with the texturedsurface along the scan path; and the textured surface along the scanpath that reacts with the surface modifier has at least one of a watercontact angle when exposed to water of at least 120° and a spectralreflectance of less than 25% within the visible spectrum.

Embodiment 12 relates to the surface modified metal piece of Embodiment11, wherein the laser power intensity is from 0.2 GW/cm² to about 20GW/cm².

Embodiment 13 relates to the surface modified metal piece of Embodiments11-12, wherein the textured surface along the scan path that reacts withthe surface modifier has a water contact angle when exposed to water ofat least 150°

Embodiment 14 relates to the surface modified metal piece of Embodiments11-13, wherein the metal piece is made of steel, titanium, aluminum,magnesium, and alloys thereof.

Embodiment 15 relates to the surface modified metal piece of Embodiments11-14, wherein the metal piece is AISI 4130 steel, titanium Ti-6Al-4Valloy (Ti-6Al-4V), aluminum alloy 6061 alloy (AA-6061) or magnesiumAZ31B alloy (Mg AZ31B).

Embodiment 16 relates to the surface modified metal piece of Embodiments11-15, wherein the surface modifier is the reaction product of a silaneof the formula:

X¹ ₃SiR′¹

wherein each X¹ is halogen or a C₁-C₆-alkoxy group; and R¹ is aC₈-C₂₀-fluoro-substituted alkyl group; and reactive sites on a majorsurface of the metal piece.

Embodiment 17 relates to the surface modified metal piece of Embodiment16, wherein R¹ is a group having the formulaC_(n)—F_(2n+1)—(CH₂)₂-(organofunctional group), wherein the“organofunctional group” is 1H, 2H, 2H-perfluoralkyl; and n is aninteger from 8 to 20.

Embodiment 18 relates to the surface modified metal piece of Embodiments11-17, wherein the at least one portion of the first major surface has aspectral reflectance of less than 60% within the IR-A spectrum.

Embodiment 19 relates to the surface modified metal piece of Embodiments11-18, wherein the at least one portion of the first major surface has aspectral reflectance of less than 30% within the IR-A spectrum.

Embodiment 20 relates to the surface modified metal piece of Embodiments11-19, wherein the at least one portion of the first major surface has aspectral reflectance of less than 60% within the IR-B spectrum.

Embodiment 21 relates to the surface modified metal piece of Embodiments11-20, wherein the at least one portion of the first major surface has aspectral reflectance of less than 40% within the IR-B spectrum.

Embodiment 22 relates to a method of making a surface modified metalpiece, the method comprising: immersing a metal piece having a firstmajor surface in an aqueous medium; texturing at least a portion of thefirst major surface along a nanosecond laser scan path at a laserscanning time of at least about 0.25 seconds/in² to obtain a texturedmetal piece having a textured surface along the scan path; removing thetextured metal piece from the aqueous medium; and immersing the texturedmetal piece in a solution comprising a surface modifier, wherein thesurface modifier reacts with the textured surface to obtain a modifiedmetal surface; wherein: at least one of the textured surface along thescan path and the textured surface that reacts with the surface modifierhas a random micro- and nanoscale structure; the nanosecond laser emitspulses of an appropriate energy onto the first major surface along thescan path; the nanosecond laser has a laser power intensity of greaterthan about 0.2 GW/cm²; the surface modifier reacts substantially onlywith the textured surface along the scan path; and the textured surfacealong the scan path that reacts with the surface modifier has at leastone of a water contact angle when exposed to water of at least 120° anda spectral reflectance of less than 25% within the visible spectrum.

What is claimed is:
 1. A surface modified metal piece comprising: afirst major surface, wherein at least one portion of the first majorsurface: comprises the reaction product of a surface modifier; has arandom micro- and nanoscale structure; and has at least one of a watercontact angle when exposed to water of at least about 120° and aspectral reflectance of less than about 25% within the visible spectrum.2. The surface modified metal piece of claim 1, wherein the at least oneportion of the first major surface comprising the surface modifier has awater contact angle when exposed to water of at least 150°.
 3. Thesurface modified metal piece of claim 1, wherein the metal piece is madeof steel, titanium, aluminum, magnesium, and alloys thereof.
 4. Thesurface modified metal piece of claim 1, wherein the metal piece is AISI4130 steel, titanium Ti-6Al-4V alloy (Ti-6Al-4V), aluminum alloy 6061alloy (AA-6061) or magnesium AZ31B alloy (Mg AZ31B).
 5. The surfacemodified metal piece of claim 1, wherein the surface modifier is thereaction product of a silane of the formula:X¹ ₃SiR¹ wherein each X¹ is halogen or a C₁-C₆-alkoxy group; and R¹ is aC₈-C₂₀-fluoro-substituted alkyl group; and reactive sites on a majorsurface of the metal piece.
 6. The surface modified metal piece of claim5, wherein R¹ is a group having the formulaC_(n)—F_(2n+1)—(CH₂)₂-(organofunctional group), wherein the“organofunctional group” is 1H, 2H, 2H-perfluoralkyl; and n is aninteger from 8 to
 20. 7. The surface modified metal piece of claim 1,wherein the at least one portion of the first major surface has aspectral reflectance of less than 60% within the IR-A spectrum.
 8. Thesurface modified metal piece of claim 1, wherein the at least oneportion of the first major surface has a spectral reflectance of lessthan 30% within the IR-A spectrum.
 9. The surface modified metal pieceof claim 1, wherein the at least one portion of the first major surfacehas a spectral reflectance of less than 60% within the IR-B spectrum.10. The surface modified metal piece of claim 1, wherein the at leastone portion of the first major surface has a spectral reflectance ofless than 40% within the IR-B spectrum.
 11. A surface modified metalpiece made by the process comprising: immersing a metal piece having afirst major surface in an aqueous medium; texturing at least a portionof the first major surface along a nanosecond laser scan path at a laserscanning time of at least about 0.25 seconds/in² to obtain a texturedmetal piece having a textured surface along the scan path; removing thetextured metal piece from the aqueous medium; and immersing the texturedmetal piece in a solution comprising a surface modifier, wherein thesurface modifier reacts with the textured surface to obtain a modifiedmetal surface; wherein: at least one of the textured surface along thescan path and the textured surface that reacts with the surface modifierhas a random micro- and nanoscale structure; the nanosecond laser emitspulses of an appropriate energy onto the first major surface along thescan path; the nanosecond laser has a laser power intensity of greaterthan about 0.2 GW/cm²; the surface modifier reacts substantially onlywith the textured surface along the scan path; and the textured surfacealong the scan path that reacts with the surface modifier has at leastone of a water contact angle when exposed to water of at least 120° anda spectral reflectance of less than 25% within the visible spectrum. 12.The surface modified metal piece of claim 11, wherein the laser powerintensity is from 0.2 GW/cm² to about 20 GW/cm².
 13. The surfacemodified metal piece of claim 11, wherein the textured surface along thescan path that reacts with the surface modifier has a water contactangle when exposed to water of at least 150°
 14. The surface modifiedmetal piece of claim 11, wherein the metal piece is made of steel,titanium, aluminum, magnesium, and alloys thereof.
 15. The surfacemodified metal piece of claim 11, wherein the metal piece is AISI 4130steel, titanium Ti-6Al-4V alloy (Ti-6Al-4V), aluminum alloy 6061 alloy(AA-6061) or magnesium AZ31B alloy (Mg AZ31B).
 16. The surface modifiedmetal piece of claim 11, wherein the surface modifier is the reactionproduct of a silane of the formula:X¹ ₃SiR′¹ wherein each X¹ is halogen or a C₁-C₆alkoxy group; and R¹ is aC₈-C₂₀-fluoro-substituted alkyl group; and reactive sites on a majorsurface of the metal piece.
 17. The surface modified metal piece ofclaim 16, wherein R¹ is a group having the formulaC_(n)—F_(2n+1)—(CH₂)₂-(organofunctional group), wherein the“organofunctional group” is 1H, 2H, 2H-perfluoralkyl; and n is aninteger from 8 to
 20. 18. The surface modified metal piece of claim 11,wherein the at least one portion of the first major surface has aspectral reflectance of less than 60% within the IR-A spectrum.
 19. Thesurface modified metal piece of claim 11, wherein the at least oneportion of the first major surface has a spectral reflectance of lessthan 30% within the IR-A spectrum.
 20. The surface modified metal pieceof claim 11, wherein the at least one portion of the first major surfacehas a spectral reflectance of less than 60% within the IR-B spectrum.21. The surface modified metal piece of claim 11, wherein the at leastone portion of the first major surface has a spectral reflectance ofless than 40% within the IR-B spectrum.
 22. A method of making a surfacemodified metal piece, the method comprising: immersing a metal piecehaving a first major surface in an aqueous medium; texturing at least aportion of the first major surface along a nanosecond laser scan path ata laser scanning time of at least about 0.25 seconds/in² to obtain atextured metal piece having a textured surface along the scan path;removing the textured metal piece from the aqueous medium; and immersingthe textured metal piece in a solution comprising a surface modifier,wherein the surface modifier reacts with the textured surface to obtaina modified metal surface; wherein: at least one of the textured surfacealong the scan path and the textured surface that reacts with thesurface modifier has a random micro- and nanoscale structure; thenanosecond laser emits pulses of an appropriate energy onto the firstmajor surface along the scan path; the nanosecond laser has a laserpower intensity of greater than about 0.2 GW/cm²; the surface modifierreacts substantially only with the textured surface along the scan path;and the textured surface along the scan path that reacts with thesurface modifier has at least one of a water contact angle when exposedto water of at least 120° and a spectral reflectance of less than 25%within the visible spectrum.